PROJECT SUMMARY/ABSTRACT Glutamate receptors mediate excitatory responses in the mammalian central nervous system, and ultimately control motor and cognitive functions. Glutamate receptors are classified into three subfamilies based on affinity profiles for several synthetic and natural agonists: N-methyl-D-aspartate (NMDA), ?-amino-5-methyl-3- hydroxy-4-isoxazole propionate (AMPA) and kainate receptors. All three subtypes are broadly similar having a dimer of dimer architecture with similar topologies. However, their gating characteristics and mechanisms are unique resulting in unique roles in synaptic transmission. The work in my laboratory focuses on understanding the mechanisms underlying the fine-tuning of each of these subtypes. AMPA receptors mediate fast synaptic transmission and their gating properties are modulated by the presence of auxiliary subunits (TARPs) as well as through post-translational modifications. Work from my laboratory has provided insight into the mechanism of activation and desensitization in AMPA receptors using a combination of biophysical and biochemical methods. Here, we propose to study how these mechanisms can be translated to modulation by TARPs and post-translational modifications such as phosphorylation. For this we will use a combination of smFRET and LRET to determine the dynamics and conformational changes, and validate these structure-dynamic changes through functional characterization of changes elicited by biochemical manipulations of the receptor like cross linking and mutations. The NMDA receptors, on the other hand, mediate Ca2+ permeable long depolarizing signals and are modulated through small molecule modulators, phosphorylation and interacting partners such as calmodulin and alpha-actinin at the intracellular carboxy terminus. smFRET and LRET investigations from my laboratory as well as the X-ray and EM structures have provided significant insight into conformational changes within the ordered extracellular domains. However, the communication across domains and the role of the disordered C-terminal domain are largely unexplored. Here we propose to study the role of interactions across domains in controlling dynamics and conformational changes in the receptor, and effects of modulators and changes at the C-terminal domain on these interactions and conformational dynamics. These studies will then be correlated to functional consequences thus providing insight into the structure-dynamic pathway of activation, desensitization, and modulation in these receptors.